As an important type of vacuum heat treatment equipment, the core advantage of the gas quenching furnace lies in the rapid cooling of workpieces through gas medium, and the selection of gas directly affects the quenching effect, workpiece performance and production cost. Taicang Huarui Vacuum Furnace Industry Co., Ltd. has conducted in-depth research on the physical properties and process compatibility of different gases in the research and development and manufacturing of gas quenching furnaces. It has formed a scientific gas selection scheme, providing targeted gas quenching solutions for various industries to ensure that the equipment can perform stably in different application scenarios.
The core basis for gas selection in gas quenching furnaces
The selection of gas for a gas quenching furnace needs to comprehensively consider four major factors: cooling rate, material properties of the workpiece, process requirements, and economy. These factors are interrelated and jointly determine the compatibility of the gas medium. The cooling rate is the primary indicator for gas selection, which depends on the gas's thermal conductivity, density and flow rate. Gases with high thermal conductivity can remove the heat from the surface of workpieces more quickly. For instance, the thermal conductivity of helium is over six times that of nitrogen, and under the same pressure, its cooling rate is significantly faster. Gases with higher density (such as argon) can form a denser gas flow layer under high pressure, enhancing the heat exchange efficiency with the surface of the workpiece. The flow rate is related to the fan power and the flow guide structure of the gas quenching furnace. Generally, the higher the gas pressure (0.1-0.6MPa), the faster the flow rate, and the cooling speed also increases accordingly. The gas quenching furnace of Taicang Huarui Vacuum Furnace Industry Co., Ltd. can increase the gas flow rate by 30% by optimizing the Angle of the fan blades and the design of the furnace chamber deflector plate, further improving the cooling efficiency under the same gas medium. The hardenability of the workpiece material determines the minimum requirement for the cooling rate. Materials such as high-carbon steel and high-speed steel require a relatively fast cooling rate to obtain a martensitic structure. Insufficient cooling can lead to the formation of pearlite, affecting hardness. However, low-carbon alloy steel, titanium alloy and other materials have relatively low requirements for cooling speed. Excessive cooling may cause cracks. For instance, Cr12 die steel requires a cooling rate of over 50℃/s to be hardened, while the gas quenching cooling rate of 304 stainless steel can be controlled at 10-20℃/s to meet the performance requirements. The temperature range in the process requirements also affects the selection of gases. In high-temperature zones above 600℃, the thermal radiation effect of gases intensifies, and at this time, gases with high thermal conductivity have a more obvious cooling advantage. In the low-temperature zone below 300℃, convective heat transfer becomes dominant, and the influence of gas density is even greater.
In addition, for workpieces with brightness requirements (such as precision gears), gases with a purity of ≥99.99% should be selected to prevent impurity gases from reacting with the workpiece surface at high temperatures to form color spots. Economy is a factor that cannot be ignored in large-scale production. Although rare gases (helium, neon) have excellent cooling performance, they are expensive and are suitable for small-batch high-precision parts. Industrial gases such as nitrogen and argon are relatively low in cost and easy to obtain, making them more suitable for mass production. The gas quenching furnace of Taicang Huarui Vacuum Furnace Industry Co., Ltd. supports the mixed use of multiple gases. By adjusting the proportion of nitrogen and helium, it can reduce costs while meeting the cooling speed requirements. For example, adding 20% helium to nitrogen can increase the cooling speed by 40%, while the cost is only one-third of that of pure helium.
The characteristics and applicable scenarios of commonly used gas quenching gases
Due to the differences in physical properties, different gas media have formed their own applicable fields in the gas quenching process. Understanding these characteristics is helpful for precisely matching production demands.
Nitrogen: A balance between versatility and economy
Nitrogen is a widely used gas in gas quenching furnaces. It is abundant in sources (extracted from air separation), low in cost (about half that of argon), and chemically stable, not reacting with metals at high temperatures. The cooling rate of nitrogen is moderate. Under a pressure of 0.5MPa, the cooling rate of a 50mm thick 45# steel sample is approximately 25℃/s. It is suitable for materials with good hardenability such as alloy structural steel and stainless steel. In the production of automotive parts, nitrogen gas quenching is widely used for the quenching treatment of transmission gears. A certain automotive gear factory adopted the Huarui gas quenching furnace to treat 20CrMnTi gears with 0.4MPa nitrogen. After heating to 880℃ and holding at that temperature, the gears were cooled to below 200℃ with nitrogen. The surface hardness of the gears reached HRC58-60, and the core hardness was HRC35-40, meeting the comprehensive requirements of wear resistance on the tooth surface and impact resistance in the core. The deformation of gears after nitrogen gas quenching is ≤0.03mm. There is no need for subsequent straightening processes, and they can directly enter grinding processing, increasing production efficiency by 20%. Another advantage of nitrogen is that it can enhance the cooling effect by increasing the pressure. When the pressure is raised from 0.1MPa to 0.6MPa, the cooling rate can double, which can meet the quenching requirements of some high-speed steels. The gas quenching furnace of Taicang Huarui Vacuum Furnace Industry Co., Ltd. supports stepless adjustment of nitrogen pressure and is combined with a staged cooling process (rapid cooling at 0.6MPa in the high-temperature section and slow cooling at 0.2MPa in the low-temperature section), which can reduce the internal stress of the workpiece while ensuring hardness.
Argon: Precise cooling under high-purity protection
Argon is an inert gas with a density 1.38 times that of nitrogen. Under the same pressure, it exerts a greater impact force on workpieces and has a cooling rate 15% to 20% higher than that of nitrogen. One of its major advantages is that its purity is easy to guarantee (industrial pure argon purity ≥99.99%), and it does not react with any metal, making it particularly suitable for precision parts with strict surface quality requirements. In the aerospace field, argon gas quenching is often used for the heat treatment of titanium alloy parts. Titanium alloys are prone to absorbing oxygen and nitrogen at high temperatures, leading to embrittlement. However, the high purity of argon can effectively isolate impurities and protect the surface of parts. A certain aviation enterprise adopted the Huarui gas quenching furnace to treat TC4 titanium alloy blades with 0.5MPa argon gas. After heating to 920℃ and holding at that temperature, the cooling rate of the argon gas was controlled at 15℃/s. The surface roughness of the blades was Ra≤0.8μm, without oxidation color, and the mechanical properties met the standards (tensile strength ≥900MPa). Meet the requirements of lightweight and high reliability for aircraft. The high-density characteristic of argon gas gives it a significant advantage when processing large-sized and thick-walled workpieces. For instance, when processing a 300mm diameter die steel module, argon gas can form a stable gas flow layer on the module surface, ensuring that the cooling rate difference between the center and the surface is ≤5℃/s, thus avoiding cracking caused by uneven cooling. The argon-specific gas quenching furnace designed by Taicang Huarui Vacuum Furnace Industry Co., Ltd. for thick-walled workpieces adopts a vertical gas flow circulation with air intake from the bottom and exhaust from the top, which improves the cooling uniformity of thick and large workpieces by 40%.
Helium: Special requirements for efficient cooling
Helium has the highest thermal conductivity among all gases. Its cooling rate is 5 to 6 times that of nitrogen. At a pressure of 0.3MPa, it can achieve the cooling rate required for quenching high-speed steel (≥60℃/s). However, it is expensive (about 20 times that of nitrogen) and is mostly used for processing special materials or high-precision parts. Gas quenching of high-speed steel cutting tools is a typical application scenario of helium. W6Mo5Cr4V2 high-speed steel cutting tools need to be rapidly cooled to obtain a fine martensitic structure, ensuring the hardness of the cutting edge (HRC63-65) and red hardness. A certain tool factory uses Huarui gas quenching furnaces to treat φ10mm end mills with 0.4MPa helium gas. It only takes 80 seconds to cool from 1200℃ to 200℃. There is no decarburization on the cutting edge, the metallographic structure is uniform, and the cutting life is 30% longer than that of oil-quenched tools. Another application of helium is the quenching of thin-walled precision parts. Its low density property can reduce the impact of gas flow on the parts and prevent deformation. For instance, in the electronics industry, precision spring plates (with a thickness of 0.1mm) are quenched with helium gas, which offers rapid and uniform cooling. The flatness error of the spring plates is ≤0.02mm, far superior to the 0.05mm quenched with nitrogen gas. The helium recovery system of Taicang Huarui Vacuum Furnace Industry Co., Ltd. can increase the gas utilization rate to 90%, reduce helium consumption through recycling, and lower the operating cost by 60%.
Mixed gas: An optimized balance between performance and cost
By adjusting the proportion of nitrogen, argon and helium in the mixed gas, the cooling rate can be precisely controlled, taking into account both performance and economy, making it an ideal choice for complex processes. Nitrogen-helium mixed gas (with helium accounting for 20% to 30%) is widely used in the processing of die steel. For instance, Cr12MoV die steel requires a cooling rate of 35℃/s, while pure nitrogen (0.6MPa) only has a cooling rate of 28℃/s, which fails to meet the requirements. By using a mixed gas of 30% helium and 70% nitrogen, the cooling rate can reach 38℃/s, and the cost is only one fourth of that of pure helium. After a certain mold enterprise adopted this solution, the hardness compliance rate of the molds increased from 85% to 99%, and the scrap rate was significantly reduced. A mixed argon-nitrogen gas (with argon accounting for 50%) is suitable for bright quenching of stainless steel. Stainless steel may undergo trace nitriding when cooled in nitrogen, which affects its corrosion resistance. However, adding argon can dilute the nitrogen concentration and reduce the nitriding reaction. A certain medical device enterprise treated 316L stainless steel surgical forceps with this mixed gas. The surface was as bright as a mirror. After 72 hours of salt spray testing, there was no rust, meeting the medical-grade hygiene requirements. The gas quenching furnace of Taicang Huarui Vacuum Furnace Industry Co., Ltd. is equipped with an automatic gas distribution system, which can automatically adjust the gas ratio according to the preset process parameters, with an accuracy controlled within ±2%. The system is equipped with 100 sets of mixed gas formulas, covering a wide range of materials from low alloy steel to high-speed steel. Operators can directly invoke them without manual blending, ensuring process stability.
Application scenarios of gas quenching gases in typical industries
Due to the differences in material properties and product requirements, various industries have developed distinctive gas selection schemes for gas quenching. These schemes have been verified through practice and provide reference examples for similar enterprises.
Automotive parts industry: Batch processing mainly based on nitrogen
Automotive gears and shaft parts mostly use alloy structural steels such as 20CrMnTi and 40Cr. Due to cost sensitivity and the need for mass production, nitrogen has become the mainstream choice. The production line of a certain automotive transmission factory is equipped with 10 Huarui gas quenching furnaces, all of which use 0.5MPa nitrogen to treat gears, with a daily processing capacity of up to 5,000 pieces. The hardness of gears quenched by nitrogen gas is uniform (HRC58±1), with small deformation. Combined with an automatic loading and unloading system, the entire process of "heating - quenching - cleaning" is fully automated, and the energy consumption per unit product is reduced by 30% compared with salt bath quenching. For some safety components with higher requirements (such as steering knuckles), a mixed gas of nitrogen and 10% helium is used to ensure the cooling speed while controlling the cost. The tensile strength of the treated steering knuckle has increased by 15%, and its impact toughness reaches 80J/cm², meeting the requirements of automotive safety crash tests.
Mold manufacturing industry: Precise matching of argon gas and mixed gases
Cold working dies (such as stamping dies) commonly use Cr12MoV steel, which requires a surface hardness of ≥HRC58 and excellent wear resistance. Argon gas quenching is an ideal choice. A certain mold factory used Huarui gas quenching furnace to treat 1000×500mm stamping dies with 0.6MPa argon gas. The surface hardness of the die was HRC59-60, and the wear resistance of the working band was 40% higher than that of oil-quenched dies. The service life was extended from 80,000 times to 120,000 times. Hot working dies (such as die-casting dies) are made of H13 steel and need to balance hardness and toughness. A mixed gas of argon and nitrogen (7:3) is often selected. The cooling rate of the 0.4MPa mixed gas is controlled at 25℃/s. The hardness of the mold core is HRC45-48, and it has excellent thermal fatigue resistance. In the production of aluminum alloy die-casting, it can withstand 1,500 cycles without cracking.
Aerospace industry: Special applications of helium and high-purity argon
The turbine blades of aero engines are made of high-temperature alloys (such as GH4169), and surface contamination must be avoided during heat treatment. High-purity argon gas (99.999%) is a necessary choice. A certain aviation enterprise treated the blades with 0.5MPa high-purity argon gas from Huarui gas quenching furnace. After heating to 1080℃, the argon gas was cooled, and a dense oxide film (thickness ≤5μm) was formed on the surface of the blades, and the oxidation resistance performance met the requirements for long-term operation at 1000℃. The titanium alloy components of the missile cabin are quenched with helium gas. The cooling rate of 0.3MPa helium gas reaches 40℃/s, and the deformation of the components is ≤0.1mm/m, meeting the precise assembly requirements of the cabin with other components. The vertical gas quenching furnace designed by Taicang Huarui Vacuum Furnace Industry Co., Ltd. for this type of product adopts a vertical hoisting method for workpieces, further reducing deformation caused by gravity and increasing the qualification rate to 99%.
Tool manufacturing industry: Graded use of helium and nitrogen
High-speed steel cutting tools are selected with different gases based on their precision grades: Common milling cutters use a mixed gas of nitrogen and 20% helium, with a cooling rate of 50℃/s at a pressure of 0.4MPa and a hardness of HRC63-64, meeting general cutting requirements. Precision reamers and taps require pure helium gas quenching at a cooling rate of 70℃/s, with the cutting edge accuracy reaching IT5 grade and the surface roughness of the machined holes Ra≤0.8μm. The Huarui gas quenching furnace group of a certain tool factory adopts a "dual gas circuit" design, which can quickly switch between nitrogen and helium. The production change time has been shortened from 2 hours to 30 minutes, meeting the flexible production requirements of multiple varieties and small batches. The application of helium gas recovery systems has reduced the gas cost of a single precision tool by 50%, achieving a balance between performance and economy. The selection of gases for gas quenching furnaces is a technology that integrates science and practice. It requires flexible allocation based on an understanding of the gas's characteristics and in combination with specific application scenarios. Taicang Huarui Vacuum Furnace Industry Co., Ltd. continuously optimizes the performance of its equipment (such as higher pressure control and better gas flow circulation), constantly expanding the application boundaries of gas media, enabling the same gas quenching furnace to adapt to various process requirements of nitrogen, argon, helium and mixed gases. Whether it is mass production that pursues cost advantages or high-end manufacturing that meets strict performance requirements, a reasonable gas selection combined with high-quality gas quenching equipment can achieve the comprehensive goal of "precise control of cooling rate, stable and reliable workpiece performance, and optimized balance of production costs", promoting the development of the heat treatment industry towards high efficiency, precision and environmental protection.
